1. Field of the Invention
This invention relates to the field of radio frequency identification (RFID) devices, and specifically to methods for determining or predicting performance of such RFID devices.
2. Description of the Related Art
Radio frequency identification (RFID) tags and labels (collectively referred to herein as “devices”) are widely used to associate an object with an identification code. RFID devices generally have a combination of antennas and analog and/or digital electronics, which may include for example communications electronics, data memory, and control logic. For example, RFID tags are used in conjunction with security locks in cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,262,692, all of which are hereby incorporated by reference in their entireties.
As noted above, RFID devices are generally categorized as labels or tags. RFID labels are RFID devices that are adhesively or otherwise have a surface attached directly to objects. RFID tags, in contrast, are secured to objects by other means, for example by use of a plastic fastener, string or other fastening means.
RFID devices include active tags and labels, which include a power source, and passive tags and labels, which do not. In the case of passive tags, in order to retrieve the information from the chip, a “base station” or “reader” sends an excitation signal to the RFID tag or label. The excitation signal energizes the tag or label, and the RFID circuitry transmits the stored information back to the reader. The “reader” receives and decodes the information from the RFID tag. In general, RFID tags can retain and transmit enough information to uniquely identify individuals, packages, inventory and the like. RFID tags and labels also can be characterized as to those to which information is written only once (although the information may be read repeatedly), and those to which information may be written during use. For example, RFID tags may store environmental data (that may be detected by an associated sensor), logistical histories, state data, etc.
It is often desirable to test the performance of RFID devices to ensure acceptable levels of performance. Such tests have often been performed under controlled simulated conditions. For example, tags may be individually tested at a distance similar to that expected in actual use of the tag, in order to determine if the tag or other device performs acceptably.
There are several potential problems with this sort of testing. First, such testing requires a relatively large space. Second, the process does not support a high volume manufacturing environment. Third, the results of such testing may be affected by a variety of factors, such as changes in the environment around the tested RFID device. This may result in a need for careful control of the environment in which the testing is performed, for example by maintaining position of any electrically conductive items in the vicinity of the test. In order to maintain repeatability of testing, it may be desirable to utilize test chambers that isolate the tested device from the surrounding environment. It will be appreciated that under some circumstances it may be necessary to isolate devices individually when performing testing, in order to prevent the response from one RFID device with interfering with the response from other nearby devices. Thus, it will be appreciated that performing such testing on closely spaced devices, such as devices on a sheet or a roll, may be impractical and/or expensive.
From the preceding, it will be appreciated that improvements in testing of RFID devices would be desirable.